1. Field of Invention
The invention relates to, in general, a diagnosis method and control unit for performing a diagnosis and, in particular, a diagnosis of a lambda sensor of the “UEGO” type of an exhaust system for an internal-combustion engine.
2. Description of Related Art
A lambda sensor of the “UEGO” (Universal Exhaust Gas Oxygen) type (also known as “linear oxygen sensor”), which provides a measurement of the oxygen content present in the exhaust gases, is used in an exhaust system for an internal-combustion engine.
The measurements provided by the lambda sensor of the “UEGO” type are used by the engine-control unit for adjusting the combustion in the cylinders of the internal-combustion engines to minimize the generation of polluting substances. It is, thus, apparent that if, following a fault, the lambda sensor of the “UEGO” type supplies incorrect measurements of the oxygen content present in the exhaust gases to the engine control, the engine control will incorrectly adjust the combustion in the cylinders of the internal-combustion engine, and, thus, an even very high increase of the generation of polluting substances will occur. Therefore, type-approval standards require to continuously diagnose the correct operation of the lambda sensor of the “UEGO” type to rapidly intervene with recovery strategies in case of malfunctioning of the lambda sensor of the “UEGO” type.
Currently, the known diagnosis of a lambda sensor of the “UEGO” type includes searching for the presence of a short circuit to a battery, the presence of a short circuit to ground, and the presence of an open (interrupted) circuit. However, the known diagnosis of a lambda sensor of the “UEGO” type allows the presence of a short circuit or of an open circuit to be identified, but does not allow to fully discriminate which type of fault is present and on which pin of the lambda sensor of the “UEGO” type the fault occurred.